I think it probably came from Russia
It fits a Russian modus operandi
They no doubt knew it would be identified and that diplomatic expulsions would result, this may in fact have been the desired result, for reasons that are not yet apparent

Smoke and mirrors.

I expect my government to be righteous in their indignation.
Im allowed to be cynical, they are not.
We want peace in this world then all of us that think the same, have the same values, should always strive for peace publicly.

They reacted like it was a state sponsored act of war.
The daughter is recovering, but the dad is still on life support. If the russians want you dead, you are dead. Just like if the brits want you dead, you are dead. Its a matter of how not if.